1883. | The Hair-Sac Mite of the Pig. 1115 
The following are the appendages attached to the cephalic seg- 
ment: 
Ist. A pair of mandibles seen best from the dorsal surface and 
resembling a pair of scissors of which both the blades are ter- 
minated by blunt points. . 
2d. A pair of maxillæ which lie in a depression on the under 
surface of the cephalic segment: 
3d. A pair of pedipalpi which are three-jointed, the middie 
joint being soft while the last bears three incurved hooks. 
4th. An unpaired stylet seen only from the ventral surface be- 
tween the maxilla, which appears to be connected with the pharynx. 
The appendages of the mouth move chiefly horizontally, and 
are therefore of a masticatory nature, but the closed maxilla form 
a sharp point anteriorly and thus form a piercing organ. 
Some interesting particulars are given as to the development of 
the cephalic segment and its appendages. The clear anterior 
end of the egg is rounded off as the head segment, and already 
the pedipalpi and the future eyes may be seen; the depression 
ween the pedipalpi is then occupied by the outgrowth of a 
pyramid which by a cleft in the middle line and a further longi- 
tudinal division of each of the resulting halves is converted into 
the mandibles externally and the maxillæ internally. 
The pharynx is lined with chitin, and a short cesophagus leads 
from it to the stomach, which occupies the greater part of the 
thorax and which is seen in optical section to possess a. wavy 
contour. Csokor considers this to be due to gastric coeca such 
às are generally present in the Arachnida. The short intestine 
Opens on the ventral surface behind the sternum in a fissure, which 
's twice as long in the female as it is in the male. 
_ A group of refractive particles in the end of the abdomen are 
interpreted as urinary concretions; they are to be traced also in 
the earlier stages of development. : 
In stained specimens a rudimentary tracheal system 1s to be 
detected from the dorsal surface, composed of two longitudinal 
canals running back as far as the last pair of legs. These canals 
ve a few branches and may possibly open on the exterior by 
certain little protuberances which have already been described 
Leydig and Megnin. 
Two little crescentic bodies, further back upon the dorsal sur- 
face, are interpreted as rudimentary circulatory organs. 
Vi 
OL, XVII,—No, 2 74 
